Epidemic Typhus Associated with Flying Squirrels -- United States

Since 1976, 30 cases of illness caused by Rickettsia
prowazekii,
the causative organism of epidemic typhus, have been documented
serologically among residents of the United States (1-3). These
cases
have been unusual in that, unlike classic louse-borne epidemic
typhus,
they have occurred sporadically, primarily in rural or suburban
areas
of the eastern United States. Ten of the 30 cases have occurred in
Georgia, four in Virginia, three in North Carolina, two in
Pennsylvania, two in Indiana, and one each in California, Illinois,
Maryland, Massachusetts, Ohio, New Jersey, New York, Tennessee, and
West Virginia. Twenty-one of the 30 cases have occurred during the
coldest months of the year--December, January, and February (Figure
1).

Of the 30 patients with sporadic R. prowazekii infection, 73%
have
been greater than or equal to 20 years of age and 50% have been
male. Clinically, patients have presented with fever (100%),
headache
(81%), skin rash (66%), confusion (44%), and myalgia (42%). The
skin
rash has been characterized as maculopapular, usually involving the
trunk and spreading to the extremities. Seventy-six percent of
patients have received therapy with tetracycline or
chloramphenicol;
recovery has been much more rapid among these patients than among
those not receiving appropriate antibiotics. However, no patient
with
sporadic R. prowazekii infection, regardless of antibiotic therapy,
has died.

In 10 of 18 cases of sporadic R. prowazekii infection for which
information has been available, flying squirrels, or nests
consistent
with those observed for flying squirrels, have been found in a home
or
building frequented by the patient. In one report, the southern
flying squirrel, Glaucomys volans, was readily trapped in the
environs
of the patient in six of seven cases (2). This rodent inhabits the
eastern United States, frequently nests in the attics of houses
during
the winter, and is a known host of R. prowazekii (4). It is
presumed
that infection is acquired from this animal, although the mechanism
of
transmission is unknown. One case of typhus occurred in
California,
where G. volans is absent. Glaucomys sabrinus, a close relative of
G.
volans, is present in California, but serologic studies of this
species for antibody to R. prowazekii have been initiated only
recently.

It has long been assumed that the causative agent of epidemic
typhus existed only in the man-louse-man cycle, and that patients
who
had recovered from typhus constituted the reservoir of R.
prowazekii
in inter-epidemic periods (rickettsemia develops in Brill-Zinsser
disease, the recrudescent form of R. prowazekii infection). Under
this assumption, eradication of epidemic typhus on a global scale
would be theoretically possible, since few patients with
Brill-Zinsser
disease would be alive after long inter-epidemic periods. The
finding
of sporadic R. prowazekii infecton and the existence of a sylvan
reservoir of this rickettsial agent, therefore, have important
implications concerning the perpetuation of epidemic typhus in
humans. Since none of the patients with sporadic epidemic typhus
have
been infested with body lice, the possibility that sporadically
acquired infection can precipitate outbreaks of epidemic typhus
remains unexplored. Whether flying squirrels and/or other
mammalian
hosts were infected with R. prowazekii before the evolution of
epidemic typhus in humans, or whether the reverse is true, is also
unknown.

Since the causative organism has yet to be isolated from a
human
with sporadic R. prowazekii infection and since the mechanism of
transmission of this disease has not been elucidated, CDC is
attempting to identify as many cases of this disease as possible.
Therefore, physicians who encounter patients with a
rickettsial-like
illness (fever, headache, myalgia, and skin rash) during the colder
months are encouraged to report these cases to CDC through their
local
and state health departments.
Reported by Div of Viral Diseases, Center for Infectious Diseases,
CDC.

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